The electrical potential that forms at the phase boundary between an electrode and the surrounding electrolyte is called electrode potential. The electrode potential of an individual electrode cannot be determined electrochemically, since a second electrode is required for potential measurement, at which an electrode potential is also formed. The measured voltage is therefore the difference between these two electrode potentials. Electrode potentials are usually measured against a reference electrode. With currentless measurement, the electrode potential corresponds to the equilibrium potential. The electrode potential of an electrode through which current flows is additionally determined by overvoltages.